Oil-injection rotary compressors such as screw compressors of the SRM type, also known as Lysholm or twin-screw compressors, are usually provided with an oil separator, either connected separately in the system in which the compressor operates or, in some cases, integrated with the compressor.
Referring to FIG. 1 of the accompanying drawings, the purpose of an oil separator is to remove oil from an operating medium and return it to the lubricant circuit 13 and any cooling circuits of a compressor 15, as well as ensuring that the operating medium passed out into the system is not too oily.
A separate oil separator 16 is usually located after the compressor 15 on the high-pressure side. It is therefore dimensioned for high operating pressure as well as generally being relatively large. These two factors make it relatively expensive and cumbersome.
As stated above, the primary task of the oil is to lubricate the movable parts of the compressor. Secondary duties are sealing and cooling.
The objective is therefore first and foremost to ensure that sufficient oil is available for the lubrication system of the compressor. For compressors in small closed-circuit cooling or heating systems, for instance, where the risk of accumulating large volumes oil can be excluded and where the oil feedback from the system is under control, only so much oil need be removed from the operating medium and returned to the lubrication system of the compressor to ensure satisfactory functioning of the compressor. In these cases simpler and smaller oil-separation systems are adequate.